New one on me! If this is reproducible, and if you have some otherversion where it is not happening, do a bisection. If you have a setof patches that you carry on top of the stable kernel (for example, tosupport some new hardware), try reproducing on hardware that is supportednatively by 3.18.19. Either way, CONFIG_DEBUG_OBJECTS_RCU_HEAD can behelpful, as can any number of other debugging Kconfig options.